Production of ceramic bodies



United States Patent 3,516,840 PRODUCTION OF CERAMIC BODIES Walter H.Gitzen, Belleville, and George MacZura, East St. Louis, 111., assignorsto Aluminum Company of America, Pittsburgh, Pa., a corporation ofPennsylvania N0 Drawing. Original application Oct. 22, 1964, Ser. No.

405,851, now Patent No. 3,432,313, dated Mar. 11,

1969. Divided and this application Oct. 31, 1968, Ser.

The portion of the term of the patent subsequent to Mar. 11, 1986, hasbeen disclaimed Int. Cl. C04b /10 U.S. Cl. 106-65 2 Claims ABSTRACT OFTHE DISCLOSURE A mixture adapted for making ceramic articles, saidmixture composed of 20-80% alumina particles having a median particlesize of 2.5-6 microns and 80-20% alumina particles having a median sizeof about 1 micron.

This is a division of US. Ser. No. 405,851 entitled Production ofCeramic Bodies, filed Oct. 22, 1964, now US. Pat. No. 3,432,3l3, issuedMar. 11, 1969.

This invention relates to the production of molded ceramic bodies ofalumina, and relates particularly to producing a special form of aluminafor use in making such bodies.

It is an object of the invention to produce improved molded bodies ofalumina which can be fired at relatively low temperatures to form dense,non-porous ceramic articles. It is a further object of the invention toprovide an improved form of alumina, of high ceramic reactivity, for usein making ceramic bodies.

It is known to make ceramic articles, such as spark plug insulators andthe like, by well-known procedures consisting of filling a mold cavitywith finely divided material, such as alumina, compressing the finelydivided material in the mold under high pressure, and firing the moldedbody at high temperature. For example, Pats. 2,091,569, 2,152,738 and2,618,567 describe procedures of that type. When using alumina as thefinely divided material, it is desirable that the alumina employedprovide a dense, non-porous compressed body of low shrinkage ordistortion in firing, and have high ceramic reactivity, that is, beconvertible to a substantially non porous, fully shrunk fired body atrelatively low firing (maturing) temperatures. It is well known thatvarious fluxes can be used to lower the firing temperature of suchmolded bodies, but such fluxes introduce impurities.

In accordance with our invention, in the production of ceramic articlesof alumina by compressing finely divided alumina in a mold and firingthe molded body, the alumina employed is a blend or mixture of twocomponents, each consisting of particles of controlled sizedistribution. One component consists of alumina particles having amedian size of 2.5-6 microns, and the second consists of particleshaving a median size of about 1 micron, the components being present inthe proportions of 20-80% 'by weight of the first-mentioned componentand 80-20% by weight of the second-mentioned component. Ordinarily, thebest results are obtained with a mixture in which the said twocomponents are present in the proportions of 40-60% and 60-40%respectively.

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Statements herein as to median sizes of particles refer to sizedeterminations on the basis of a size distribution of 8-10 sieveintervals /2 series).

Alumina hydrate made by the conventional so-called Bayer Processconsists of small particles composed of agglomerates of smallcrystallites. Crystalline alumina particles in the above-mentioneddesired sizes can be produced conveniently by heating such aluminahydrate particles in accordance with well-known procedures to convertthem to alumina composed of agglomerates of crystallites of the desiredsizes, and thereafter breaking up those agglomerates into their ultimatecrystallites, as by grinding the alumina particles in accordance withwellknown procedures. The two components may be blended in theabove-mentioned desired proportions before or after such grinding; it isusually more convenient to effect the blending before grinding.

With the alumina mixtures described herein, high density, non-porousmolded bodies which undergo low shrinkagewhen fired can readily beproduced by pressure molding. Moreover, the pressure-molded bodies canbe fired satisfactorily at temperatures as low as 1700 C., or evensomewhat lower, without using a flux in the mix.

The advantages of using alumina in the particle size distribution of ourinvention are indicated in the table below which shows propertiesobtained with six different mixtures of two components, one beingalumina particles of a median size of about 1 micron, and the otherbeing alumina particles of a median size of about 3 microns, eachcomponent being present in the percentages by weight shown in the table.Each of the mixtures was pressed at a pressure of 5,000 p.s.i. in a moldto produce round slugs 1 inch in diameter and A1 inch high, after whichthe slugs were converted to ceramic bodies by heating them for one hourat 1700 C.

Blend composition Density, g./ml.

Percent Percent Percent 1 micron 3 microns shrink- (median) (median)Pressed Fired age The above table shows that compositions 2, 3, 4 and 5containing 20-80% of particles about 3 microns in size, the balancebeing about 1 micron in size, afiorded significantly improved propertiesas compared with compositions 1 and 6.

Similar advantages were likewise obtained in a further test withcompositions which were the same as Nos. 1, 2, 3, 4, 5 and 6 of theabove table, except that each also contained 0.5% talc as a flux mixedwith the alumina.

We claim:

1. A composition adapted for use in making pressuremolded, fired ceramicbodies comprising a mixture of two separate alumina components, one ofsaid components consisting of alumina particles having a median size of2.5-6 microns, and the other of said components consisting of aluminaparticles having a median size of about 1 micron, the saidfirst-mentioned component constituting 20-80% by weight of the mixture,and the said secondmentioned component constituting 80-20% by Weight ofthe mixture.

3 2. The composition of claim 1 wherein the mixture consists of 40-60%by weight of particles of the said firstmentioned component and 60-40%by Weight of particles of the said second-mentioned component.

References Cited UNITED STATES PATENTS 8/1960 Csordas et a1. 106 -65 4Getty 106-65 Lauder et a1. 10665 Braunwarth et a1. 106-6-5 Klingler eta1. 10665 Gitzen et a1. 106--65 JAMES E. POER, Primary Examiner

